Prepare wpiutil for merge into allwpilib.

wpiutil/src/test/native/cpp/priority_mutex_test.cpp

@@ -0,0 +1,271 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2016-2018 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <support/priority_mutex.h>  // NOLINT(build/include_order)
+
+#include <atomic>
+#include <condition_variable>
+#include <thread>
+
+#include "gtest/gtest.h"
+
+namespace wpi {
+
+#ifdef WPI_HAVE_PRIORITY_MUTEX
+
+using std::chrono::system_clock;
+
+// Threading primitive used to notify many threads that a condition is now true.
+// The condition can not be cleared.
+class Notification {
+ public:
+  // Efficiently waits until the Notification has been notified once.
+  void Wait() {
+    std::unique_lock<priority_mutex> lock(m_mutex);
+    while (!m_set) {
+      m_condition.wait(lock);
+    }
+  }
+  // Sets the condition to true, and wakes all waiting threads.
+  void Notify() {
+    std::lock_guard<priority_mutex> lock(m_mutex);
+    m_set = true;
+    m_condition.notify_all();
+  }
+
+ private:
+  // priority_mutex used for the notification and to protect the bit.
+  priority_mutex m_mutex;
+  // Condition for threads to sleep on.
+  std::condition_variable_any m_condition;
+  // Bool which is true when the notification has been notified.
+  bool m_set = false;
+};
+
+void SetProcessorAffinity(int32_t core_id) {
+  cpu_set_t cpuset;
+  CPU_ZERO(&cpuset);
+  CPU_SET(core_id, &cpuset);
+
+  pthread_t current_thread = pthread_self();
+  ASSERT_EQ(pthread_setaffinity_np(current_thread, sizeof(cpu_set_t), &cpuset),
+            0);
+}
+
+void SetThreadRealtimePriorityOrDie(int32_t priority) {
+  struct sched_param param;
+  // Set realtime priority for this thread
+  param.sched_priority = priority + sched_get_priority_min(SCHED_RR);
+  ASSERT_EQ(pthread_setschedparam(pthread_self(), SCHED_RR, &param), 0)
+      << ": Failed to set scheduler priority.";
+}
+
+// This thread holds the mutex and spins until signaled to release it and stop.
+template <typename MutexType>
+class LowPriorityThread {
+ public:
+  explicit LowPriorityThread(MutexType* mutex)
+      : m_mutex(mutex), m_hold_mutex(1), m_success(0) {}
+
+  void operator()() {
+    SetProcessorAffinity(0);
+    SetThreadRealtimePriorityOrDie(20);
+    m_mutex->lock();
+    m_started.Notify();
+    while (m_hold_mutex.test_and_set()) {
+    }
+    m_mutex->unlock();
+    m_success.store(1);
+  }
+
+  void WaitForStartup() { m_started.Wait(); }
+  void release_mutex() { m_hold_mutex.clear(); }
+  bool success() { return m_success.load(); }
+
+ private:
+  // priority_mutex to grab and release.
+  MutexType* m_mutex;
+  Notification m_started;
+  // Atomic type used to signal when the thread should unlock the mutex.
+  // Using a mutex to protect something could cause other issues, and a delay
+  // between setting and reading isn't a problem as long as the set is atomic.
+  std::atomic_flag m_hold_mutex;
+  std::atomic<int> m_success;
+};
+
+// This thread spins forever until signaled to stop.
+class BusyWaitingThread {
+ public:
+  BusyWaitingThread() : m_run(1), m_success(0) {}
+
+  void operator()() {
+    SetProcessorAffinity(0);
+    SetThreadRealtimePriorityOrDie(21);
+    system_clock::time_point start_time = system_clock::now();
+    m_started.Notify();
+    while (m_run.test_and_set()) {
+      // Have the busy waiting thread time out after a while.  If it times out,
+      // the test failed.
+      if (system_clock::now() - start_time > std::chrono::milliseconds(50)) {
+        return;
+      }
+    }
+    m_success.store(1);
+  }
+
+  void quit() { m_run.clear(); }
+  void WaitForStartup() { m_started.Wait(); }
+  bool success() { return m_success.load(); }
+
+ private:
+  // Use an atomic type to signal if the thread should be running or not.  A
+  // mutex could affect the scheduler, which isn't worth it.  A delay between
+  // setting and reading the new value is fine.
+  std::atomic_flag m_run;
+
+  Notification m_started;
+
+  std::atomic<int> m_success;
+};
+
+// This thread starts up, grabs the mutex, and then exits.
+template <typename MutexType>
+class HighPriorityThread {
+ public:
+  explicit HighPriorityThread(MutexType* mutex) : m_mutex(mutex) {}
+
+  void operator()() {
+    SetProcessorAffinity(0);
+    SetThreadRealtimePriorityOrDie(22);
+    m_started.Notify();
+    m_mutex->lock();
+    m_success.store(1);
+  }
+
+  void WaitForStartup() { m_started.Wait(); }
+  bool success() { return m_success.load(); }
+
+ private:
+  Notification m_started;
+  MutexType* m_mutex;
+  std::atomic<int> m_success{0};
+};
+
+// Class to test a MutexType to see if it solves the priority inheritance
+// problem.
+//
+// To run the test, we need 3 threads, and then 1 thread to kick the test off.
+// The threads must all run on the same core, otherwise they wouldn't starve
+// eachother. The threads and their roles are as follows:
+//
+// Low priority thread:
+//   Holds a lock that the high priority thread needs, and releases it upon
+//   request.
+// Medium priority thread:
+//   Hogs the processor so that the low priority thread will never run if it's
+//   priority doesn't get bumped.
+// High priority thread:
+//   Starts up and then goes to grab the lock that the low priority thread has.
+//
+// Control thread:
+//   Sets the deadlock up so that it will happen 100% of the time by making sure
+//   that each thread in order gets to the point that it needs to be at to cause
+//   the deadlock.
+template <typename MutexType>
+class InversionTestRunner {
+ public:
+  void operator()() {
+    // This thread must run at the highest priority or it can't coordinate the
+    // inversion.  This means that it can't busy wait or everything could
+    // starve.
+    SetThreadRealtimePriorityOrDie(23);
+
+    MutexType m;
+
+    // Start the lowest priority thread and wait until it holds the lock.
+    LowPriorityThread<MutexType> low(&m);
+    std::thread low_thread(std::ref(low));
+    low.WaitForStartup();
+
+    // Start the busy waiting thread and let it get to the loop.
+    BusyWaitingThread busy;
+    std::thread busy_thread(std::ref(busy));
+    busy.WaitForStartup();
+
+    // Start the high priority thread and let it become blocked on the lock.
+    HighPriorityThread<MutexType> high(&m);
+    std::thread high_thread(std::ref(high));
+    high.WaitForStartup();
+    // Startup and locking the mutex in the high priority thread aren't atomic,
+    // but pretty close.  Wait a bit to let it happen.
+    std::this_thread::sleep_for(std::chrono::milliseconds(10));
+
+    // Release the mutex in the low priority thread.  If done right, everything
+    // should finish now.
+    low.release_mutex();
+
+    // Wait for everything to finish and compute success.
+    high_thread.join();
+    busy.quit();
+    busy_thread.join();
+    low_thread.join();
+    m_success = low.success() && busy.success() && high.success();
+  }
+
+  bool success() { return m_success; }
+
+ private:
+  bool m_success = false;
+};
+
+// TODO: Fix roborio permissions to run as root.
+
+// Priority inversion test.
+TEST(MutexTest, DISABLED_PriorityInversionTest) {
+  InversionTestRunner<priority_mutex> runner;
+  std::thread runner_thread(std::ref(runner));
+  runner_thread.join();
+  EXPECT_TRUE(runner.success());
+}
+
+// Verify that the non-priority inversion mutex doesn't pass the test.
+TEST(MutexTest, DISABLED_StdMutexPriorityInversionTest) {
+  InversionTestRunner<std::mutex> runner;
+  std::thread runner_thread(std::ref(runner));
+  runner_thread.join();
+  EXPECT_FALSE(runner.success());
+}
+
+// Smoke test to make sure that mutexes lock and unlock.
+TEST(MutexTest, TryLock) {
+  priority_mutex m;
+  m.lock();
+  EXPECT_FALSE(m.try_lock());
+  m.unlock();
+  EXPECT_TRUE(m.try_lock());
+}
+
+// Priority inversion test.
+TEST(MutexTest, DISABLED_ReentrantPriorityInversionTest) {
+  InversionTestRunner<priority_recursive_mutex> runner;
+  std::thread runner_thread(std::ref(runner));
+  runner_thread.join();
+  EXPECT_TRUE(runner.success());
+}
+
+// Smoke test to make sure that mutexes lock and unlock.
+TEST(MutexTest, ReentrantTryLock) {
+  priority_recursive_mutex m;
+  m.lock();
+  EXPECT_TRUE(m.try_lock());
+  m.unlock();
+  EXPECT_TRUE(m.try_lock());
+}
+
+#endif  // WPI_HAVE_PRIORITY_MUTEX
+
+}  // namespace wpi